Study On Influence Factors Of Tinplate Surface Wettability

Tinplate has many advantages,such as high strength,good formability,excellent corrosion resistance,innocuity and so on,it is widely used in packaging of food,beverage,and other items.However,tinplate needs to be treated with internal and external coating in the application process,and it inevitably leads to the finishing problem between the tinplate surface and the coating.The tinplate surface finishing problem is largely dependent on the surface wettability.Therefore,it is great theoretical and practical significance to study the factors influencing the tinplate surface wettability.In this paper,the influence of passivation conditions and baking on the tinplate surface wettability is studied.The difference in the composition of passivation film of tinplate with different wettability is analyzed by X-ray photoelectron spectroscopy(XPS),and the changes in the composition of passivation film of tinplate baking before and after are analyzed,the influence of tinplate passivation film composition on the wettability is studied.The effects of cold rolling method on the tinplate surface three-dimensional morphology,roughness and the surface wettability are analyzed by atomic force microscopy(AFM),and the influence of tinplate surface morphology on its surface wettability is studied by scanning electron microscopy(SEM),the following conclusions are drawn:(1)Passivation conditions have a significant effect on the tinplate surface wettability.The tinplate surface contact angle tends to decrease first and then increase with the increase of the passivation liquid temperature(25?55)?,when the passivation fluid temperature is 35?,it is smaller and the wettability is better.It also tends to decrease first and then increase with the increase of passivation liquid pH(3?5),it is smaller and wettability is better at pH=4.It tends to decrease with the increase of current density(0.2?0.4)A·cm-2.Therefore,the passivation conditions conducive to improving the tinplate surface wettability are as follows:the passivation liquid temperature is 35?,the passivation liquid pH is 4,and the passivation current density is 0.4A·cm-2.(2)The composition of the tinplate passivation film also has a significant effect on its surface wettability.The tinplate passivation film contains SnO2,SnO,Sn,Cr(OH)3,Cr2O3,Cr and H2O,and SnO2,SnO,Cr(OH)3,H2O are adverse to the tinplate surface wettability and Sn,Cr2O3 are beneficial.(3)When tinplate is baked at different temperatures and times,its surface wettability changes.The tinplate surface contact angle increases after baking 15min at 200? and 300?and decreases at 400?,500? and 600?,and it is largest 200?;it increases after baking 15min,30min and 60min at 200?,and it is largest after baking 30min.The main reason for the poor surface wettability of tinplate baked is that part of Sn is oxidized to SnO and SnO2,and the water loss of Cr(OH)3·H2O forms Cr(OH)3 in its passivation film.However,SnO,SnO2 and Cr(OH)3 are adverse to the tinplate surface wettability.(4)Tinplate product types and surface physical properties also have a significant effect on its surface wettability.The surface roughness of once cold rolling tinplate is large and uneven,while it is small and even to the twice cold rolling tinplate.Compared to the once cold rolling tinplate,the surface wettability of the twice cold rolling tinplate is better.The surface wettability of tinplate with smooth surface,small roughness,shallow rolling lines is good.